1. Field of the Invention
The present invention relates to a magnetron sputtering method for forming a soft magnetic thin film serving as a constituent of a magnetic recording head. The present invention also relates to a sputtering target for use in the magnetron sputtering method.
2. Description of the Related Art
Recently, to increase the density of magnetic recording, gaps and tracks of a magnetic head have been made narrower and recording media having a greater coercive force have been developed. As material suitable for such a magnetic head, soft magnetic thin films having high saturation magnetic flux density as well as high magnetic permeability have been developed and some of them have been already put in practical use. As magnetic heads formed of the soft magnetic thin film, there are known an MIG head and a laminated head used for recording and reproducing to a tape medium in a VTR, and a thin-film head used for recording and reproducing to a disk media in a hard disk drive.
Hitherto dominantly used soft magnetic thin films in these heads are NiFe films. Further, use may be made of FeAlSi films, Co-based amorphous films represented by a CoZrNb film and Fe nitride-based microcrystalline films represented by FeTaN and FeZrN films that are suitable for high-density recording. Some of them have been already put in practical use, and others are now in developing. Furthermore, in future, CoFe-based soft magnetic thin films are expected to be utilized. Hitherto, these soft magnetic thin films have been formed by a sputtering method, particularly, a magnetron sputtering method using an alloy target having substantially the same composition as that of a desired thin film.
The sputtering method is preferably used to form the soft magnetic thin film. This is because a CVD method is not suitable for industrial use since the raw material gas for forming a magnetic thin film in a CVD method is hardly or cannot be obtained and, even if obtained, it is highly toxic. The sputtering method is advantageous compared to other PVD methods such as a vapor deposition because magnetic properties of the soft magnetic thin film can be controlled well by the sputtering method. Of various sputtering methods available, the magnetron sputtering method is the most preferable. Unlike other sputtering methods, it can achieve industrially advantageous features such as a high deposition rate and a wide range of selectivity of materials due to less heat load given to a substrate.
However, when the magnetron sputtering method is applied to form a soft magnetic thin film for a magnetic head, it is necessary to satisfy the following technical requirements. That is, not only a high saturation magnetic flux density and high magnetic permeability should be imparted to the soft magnetic thin film for a magnetic recording head, but in-plane magnetic isotropy is required for a laminate head and appropriate in-plane magnetic anisotropy for an HDD head. Although it is possible to control the in-plane magnetic anisotropy of the soft magnetic thin film in the magnetic field during a postdeposition anneal, the in-plane magnetic anisotropy should be better to be controlled during the growth of the film from an industrial point of view. For example, in order to prevent in-plane magnetic anisotropy of an Fe nitride-based microcrystalline film for a laminated head which requires in-plane magnetic isotropy, the film is formed on a stationary substrate disposed right over a target that is subjected to sputtering erosion. This is because if a substrate is placed obliquely to the erosion portion, the microcrystalline structure of a film is also tilted to the substrate surface, with the result that undesirable in-plane magnetic anisotropy is unexpectedly generated. The in-plane magnetic anisotropy may be prevented by moving a substrate relative to a target. However, a complicated procedure is required to move the substrate. This is why this method has not yet been carried out successfully.
When the soft magnetic thin film is formed by the sputtering method, particularly, the magnetron sputtering method, under the condition that the substrate position is restricted as mentioned above, it has been found that as a target is eroded or becomes thinner, the composition of the soft magnetic thin film varies drastically. Hence, in order to form a soft magnetic thin film at a desired composition, the thickness of a target capable of sputtering may be limited to a significantly thin range. In the consequence, to make a desired film having sufficient thickness, a number of targets must be used, which inevitably increases the target cost. In addition, more time is required for exchanging a number of targets and for conditioning to remove a degraded surface phase and to stabilize the surface composition of a new target to be exchanged for. As the manufacturing time increases, a manufacturing cost raises resulting in an increase in a magnetic head price. This is a considerable problem from an industrial point of view.